Primer on Effect Sizes, Simple Research Designs, and Confidence Intervals

A Primer on Effect Sizes, Simple Research Designs, and Confidence Intervals was designed to help individuals learn to calculate effect sizes for their research designs. Effect sizes allow a clinician or researcher to determine the effect of a treatment. For example, an effect size of zero would indicate that the treatment had no effect, but generally effect sizes allow researchers to see the degree of effect of some treatment or intervention. Often, researchers and clinicians are not aware that effect sizes are connected to research designs. For years, statisticians have been aware of limits of null hypothesis significance testing (NHST). The Wilkinson Task Force (Wilkinson & Task Force on Statistical Inference, 1999) recommended that researchers report effect sizes and confidence intervals in addition to null hypothesis significance testing (NHST). The purpose of this book is to provide the connection among effect sizes, confidence intervals, and simple research designs. Also, some commonly used univariate and multivariate statistics are covered. Regression discontinuity designs, simple moderation and mediation designs, power analysis, and fit indices as effect sizes measure are presented. All calculations are demonstrated through a calculator and statistical packages such as Microsoft Excel, SPSS, SAS, Hayes' Process Analysis, and EQS. This book covers more than 25 effect sizes that are connected to simple research designs. It will be of interest to students taking a statistics class, research methods class, or research design class. Unlike many texts within this area, the current test will give students or researchers the understanding of how to calculate effect sizes with a simple calculator or with a few commands from statistical software programs. Hence, mathematical ability is not a prerequisite for this text. This text provides a nonmathematical treatment of effect sizes within the context of research designs. Finally, to aid understanding, critical material is repeated throughout this book.